The molecular biology of three different types of RNA viruses will be examined: poliovirus, vesicular stomatitis virus and Uukuniemi virus. The synthesis and function of the 3'-polyadenylic acid of poliovirus will be examined as will be the possibility that the 5'-end of the viral RNA is blocked. Poliovirus defective interfering particles will be characterized and the in vitro protein synthesis directed by poliovirus RNA will be further characterized. Work on vesibular stomatitis virus will focus on the structure of the 5'-ends of the messenger RNAs and on the possibility of extending the genetic analysis of this virus.